It is generally known that, for supporting the drying and curing processes of printing inks and especially of varnishes, dryers may be disposed at or between printing units and in the delivery area. At the same time, large amounts of primary (infrared dryer) or secondary (UV dryer) heat are delivered to the materials to be printed and to the printing machine assembly adjacent to the dryers. The amount of heat, which is emitted by convection or radiation and not used for the drying process, is regarded as a disturbance for the printing process and the sheet delivery (adversely affects the printing in the subsequent printing machinery, excessively increases the stack temperature, damages thermally sensitive material to be printed) and, moreover, adversely affects the mode of functioning of adjacent machine elements in the event that these are overheated impermissibly. In addition, all materials (cables, hoses, tubes, sensors, pneumatic cylinders, etc.) in the range of action of the dryer must be extremely heat-resistant.
Additional cooling facilities are known to prevent overheating of printing machine elements in the dryer area and to cool material to be printed.
It is known to use an aspiration device to discharge heated air from the dryer area in the sheet delivery area. However, it does not cool sheet-guiding surfaces heated by radiation.
It is also known, for example from DE 19810387 C1, that baffles can be used for guiding sheets in an effective range of dryers, on the underside of which coolant channels are disposed. However, the cooling effect is limited only to the baffles and does not extend to the adjoining machinery parts or to the material to be printed.
It is known to use cooled compressed air for cooling printing plates, for example, from EP 0480230 A1. It is also disclosed in DE 4326835 A1 to cool cylinders by means of compressed air. The compressed-air cooling apparatus, as disclosed in EP 0480230 A1, has a combination of ventilators and controlled cooling apparatuses, which are only intended to cool printing plates and are constructed as a gap nozzle with a relatively low effective range. DE 4202544 A1 and DE 4326835 A1 disclose additional compressed air cooling beams with partial circulation of the cooling air for rubber blanket or plate cylinders, which are not suitable for guiding sheets.
Furthermore, WO 01/32423 A1 discloses cooling of printing and transfer cylinders heated by dryers, as well as the materials to be printed, which are indirectly heated by the dryers, with cooled, compressed air from cooling units, which have cooling registers and ventilators and are disposed in front of the printing zone.
It is a common disadvantage of all the compressed air cooling systems mentioned above that they require additional space, which makes access to the machinery assemblies more difficult during cleaning or setting-up activities. Furthermore, they are designed only for special cooling tasks. In general, the space along the traveling path of the sheets to be printed between dryers, sheet-guiding devices, washing devices or autoregister devices is not adequate for effective cooling of the heated machine elements and of the materials to be printed, which are exposed to the dryers.